Most communications systems require a minimum signal to noise ratio (SNR) of about 10 dB (10 to 1) after signal processing and decoding in order to perform effectively. The act of jamming a signal transmits noise to a target receiver to reduce the SNR to a point at which the signal can no longer be differentiated from the noise. When performed effectively, signal jamming can be an important aspect of electronic warfare.
Here a transceiver consists of a receiver co-located with at least one transmitter. One method of jamming a target signal is for multiple friendly jamming transmitters to launch coordinated noise transmissions on frequencies the target signal may use, so as to effectively disable one or more enemy receivers. Such jamming may be directional and also require coordination of target selection in direction. In such a coordinated attack, communication between jammers both as to target selection, direction, and mode of jamming may be necessary for effective jamming. However, one challenge of jamming is that the jamming may interfere with communications of friendly transceivers. If the frequencies to be jammed are the same or near the frequencies used to communicate with friendly transceivers, jamming will have the negative consequence of interfering with or even preventing coordination and communication between such friendly transceivers.
A similar concern in jamming communications systems is known as the co-site problem. Briefly stated, all transmitters emit unwanted spurious emissions outside their intended band of operations. Large transmitters, which may be necessary in some jamming missions, have large spurious emissions. For this reason transmission sites are often located many miles from receiver sites, but this is impractical in many military operations, and is certainly impractical when a transmitter and a receiver are located on the same aircraft. In order to receive a message while jamming, an airborne transceiver may have to shut down its jamming transmissions on all frequencies—or at least on a wide band of frequencies around the frequency upon which it is desired to receive. Such a shut-down of jamming by a transmitter limits the effectiveness of the jammer. A second fellow jammer located some distance away might be able to continue jamming except on the specific frequency used for friendly communication by the first jammer. The jammer which shut down only on the friendly communications frequency would likely not be able to receive because of spurious transmissions from its own transmitter.
It is therefore an object of the invention to provide a communications system that permits communications between transceivers conducting jamming operations against a target transmitter.
It is another object of the invention to provide such a communications system that maintains signal jamming of the target signal during communications between friendly transceivers.
A feature of the invention is a jamming protocol having coordinated or synchronized silent periods during which friendly transceivers may communicate.
An advantage of the invention is that jamming missions can be effectively coordinated and maintained by multiple jamming transceivers.